W Serpentis

W Serpentis is a multiple star in the constellation Serpens. The system varies between apparent magnitudes 8.42 and 10.2 over a period of just over 14 days,[2] too faint to be seen with the unaided eye.[6] This is mainly due to the system being an eclipsing binary (that is, one star passing in front of the other star and resulting in a change in brightness). However, variations in its period indicate there are some innate changes in luminosity of one or both component stars as they interact with each other, and it has been difficult to disentangle the light to determine their nature.[7] The period is increasing by 14 seconds a year, indicating that a massive amount of material is being transferred from the larger fainter star to the smaller brighter one.[4]

W Serpentis

Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Serpens
Right ascension  18h 09m 50.64994s[1]
Declination −15° 33′ 00.2809″[1]
Apparent magnitude (V) 8.42-10.2[2]
Characteristics
Spectral type F8/G2Iaep + AV[3][4]
Variable type W Ser[5]
Astrometry
Parallax (π)0.70 ± 0.99[1] mas
Other designations
BD−15° 4842, HD 166126, HIP 88994, SAO 161128
Database references
SIMBADdata

The system has been found to contain an accretion disk, and was one of the first discovered Serpentids, which are eclipsing binaries containing exceptionally strong far-ultraviolet spectral lines.[7] These systems have a high rate of mass transfer between one star and the other, and are thought to evolve first into double periodic variables and then classical Algol variables.[8] In the late stages of mass transfer, such systems can develop an optically thick disc and are segregated as a separate class of W Serpentis stars.[5] The classes may also represent different types of system altogether, with the W Serpentis type being younger and more massive.[9]

The spectral types of the component stars are not known; the hotter brighter star has been classed as an F-type giant. However, it appears to be completely obscured by material, and another theory holds that it is a hot main sequence star with the surrounding material responsible for the spectrum as it appears to be too luminous to be an F-class star. The spectrum of the secondary (larger and fainter) star has not been detected either. Examining the polarised light shows that a jet of material is probably coming from the primary star as well.[4]

References
  1. Van Leeuwen, F. (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics. 474 (2): 653. arXiv:0708.1752. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357.
  2. VSX (4 January 2010). "W Serpentis". AAVSO Website. American Association of Variable Star Observers. Retrieved 7 July 2014.
  3. Houk, N.; Smith-Moore, M. (1988). "Michigan Catalogue of Two-dimensional Spectral Types for the HD Stars. Volume 4, Declinations -26°.0 to -12°.0". Michigan Catalogue of Two-dimensional Spectral Types for the HD Stars. Volume 4. Bibcode:1988mcts.book.....H.
  4. Piirola, V.; Berdyugin, A.; Mikkola, S.; Coyne, G. V. (2005). "Polarimetric Study of the Massive Interacting Binary W Serpentis: Discovery of High-Latitude Scattering Spot/Jet". The Astrophysical Journal. 632 (1): 576–89. Bibcode:2005ApJ...632..576P. doi:10.1086/432902.
  5. Wilson, R. E. (1989). "The Relation of Algols and W Serpentis Stars". Algols. p. 191. doi:10.1007/978-94-009-2413-0_17. ISBN 978-94-010-7587-9.
  6. Bortle, John E. (February 2001). "The Bortle Dark-Sky Scale". Sky & Telescope. Sky Publishing Corporation. Retrieved 10 July 2014.
  7. Weiland, J. L.; Shore, S. N.; Beaver, E. A.; Lyons, R. W.; Rosenblatt, E. I. (1995). "Goddard High-Resolution Spectrograph Observations of the Interacting Binary System W Serpentis". The Astrophysical Journal. 447: 401. Bibcode:1995ApJ...447..401W. doi:10.1086/175883.
  8. Mennickent, R. E.; Kolaczkowski, Z. (2009). "Interacting Binary Star Environments and the W Ser - DPV - Algol Connection". arXiv:0904.1539 [astro-ph.SR].
  9. Mennickent, R. E.; Kołaczkowski, Z. (2010). "Interacting Binary Stars Environments and the W Ser-DPV-Algol Connection". The Interferometric View on Hot Stars (Eds. Th. Rivinius & M. Curé) Revista Mexicana de Astronomía y Astrofísica (Serie de Conferencias) Vol. 38. 38: 23. arXiv:0904.1539. Bibcode:2010RMxAC..38...23M.

Further reading

https://www.eso.org/sci/publications/messenger/archive/no.39-mar85/messenger-no39-40-42.pdf

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